Regiospecificity and Stereoselectivity in the Photodimerization of 2,3-Dihydro-2,6-dimethyl-4-pyrone

1973 ◽  
Vol 51 (8) ◽  
pp. 1267-1277 ◽  
Author(s):  
Peter Yates ◽  
Donald J. MacGregor
Keyword(s):  
Aqueous Solution ◽  
Ultraviolet Irradiation ◽  
Spectroscopic Methods ◽  
Magnetic Spectrum ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Dimerization Reaction

Ultraviolet irradiation of 2,3-dihydro-2,6-dimethyl-4-pyrone in aqueous solution leads to the regiospecific and stereoselective formation of three cis–anti–cis photodimers of the cyclobutane type, i.e0., octahydro-2,7-8a,8b-tetramethylcyclobuta[1,2-b:4,3-b′]dipyran-4,5-diones, whose structures have been established by chemical and spectroscopic methods, including studies of nuclear Overhauser effects in the proton magnetic spectrum of one of them. The dimers undergo photointerconversion, and it is proposed that this process involves photoreversion to monomer and that the reversibility of the dimerization reaction may be a factor in determining the regiochemistry and stereochemistry of the photodimers. A bisdehydro product prepared from the dimers of the dihydropyrone has been shown to undergo photocleavage to 2,6-dimethyl-4-pyrone, and it is proposed that reversibility may also be a factor affecting the course of the photodimerization of this pyrone.

Nuclear Overhauser effects in aqueous solution as dynamic probes in short linear peptides

FEBS Letters ◽  
1988 ◽  
Vol 239 (1) ◽  
pp. 83-87 ◽  
Author(s):  
J.L. Nieto ◽  
M.A. Jiménez ◽  
M. Rico ◽  
J. Santoro ◽  
J. Herranz
Keyword(s):  
Aqueous Solution ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Conformation of purine mononucleotides by H{H} and P{H} nuclear Overhauser effects

1983 ◽  
Vol 61 (7) ◽  
pp. 1456-1464 ◽  
Author(s):  
H. Santos ◽  
A. V. Xavier ◽  
C.F.G.C. Geraldes
Keyword(s):  
Aqueous Solution ◽  
Nuclear Overhauser Effect ◽  
Coupling Constants ◽  
Glycosidic Bond ◽  
Proton Proton ◽  
Proton Coupling ◽  
Vicinal Proton ◽  
Group A ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

The proton–proton and phosphorus–proton nuclear Overhauser effect (nOe) of guanosine 5′-monophosphate (5′-GMP) was measured in aqueous solution at different pH values and in the presence of excess LaIII at acid pH. These data and nOe data from the literature for other mononucleotides were used together with vicinal proton–proton coupling constants to investigate the conformations of mononucleotides in aqueous solution, especially their rotational state about the glycosidic bond. Comparison of observed and calculated enhancements using various conformational models for the glycosidic bond gave predominantly anti conformations for 5′-AMP and 5′-GMP and a mixture of syn and anti conformations for 2′-AMP, 2′-GMP, 3′-AMP, and 3′-GMP. Protonation of 5′-GMP at N-7 of the guanine base alters the amplitude of its torsion angle within the anti range. The agreement between the glycosidic nucleotide conformations defined by nOe and by the lanthanide probe method is good but not perfect. As complexation of 5′-GMP with LaIII through the phosphate group has only a small effect on the conformation of its exocyclic group, a comparison of the two methods is justified.

Structures of three minor alkaloids of Fumariaofficinalis L.

1969 ◽  
Vol 47 (19) ◽  
pp. 3593-3599 ◽  
Author(s):  
D. B. MacLean ◽  
R. A. Bell ◽  
J. K. Saunders ◽  
C.-Y. Chen ◽  
R. H. F. Manske
Keyword(s):  
Ring System ◽  
Model Systems ◽  
Spectroscopic Methods ◽  
Structural Problem ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

The structures of fumaricine, fumaritine, and fumariline, minor alkaloids of F. officinalis, have been deduced by spectroscopic methods and by comparison with model systems. Nuclear Overhauser effects observed in these systems aided in the solution of the structural problem. The three alkaloids have a common ring system and are structurally related to ochotensimine.

Acetone-sensitized photodimenzation of 3-carene-2,5-dione

1970 ◽  
Vol 48 (10) ◽  
pp. 1526-1532 ◽  
Author(s):  
Ian W. J. Still ◽  
C. J. Macdonald ◽  
(Mrs.) Y.-N. Oh
Keyword(s):  
Spectroscopic Study ◽  
Ultraviolet Irradiation ◽  
Head Orientation ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Ultraviolet irradiation of 3-carene-2,5-dione 1 in acetone has been found to yield three cyclobutanetype photodimers. A detailed spectroscopic study of these compounds has shown that the two most abundant dimers possess the head-to-head orientation. The head-to-head dimers have been shown to possess the anti-anti-anti and syn-anti-syn structures 10 and 8 respectively, while the minor, head-to-tail product has one of the corresponding structures 9 or 11. In all three cases, the cyclobutane and cyclohexane rings are cis-fused. Nuclear Overhauser effects enable structures 8 and 10 to be specifically assigned to dimer B and dimer A, respectively.

scholarly journals NMR solution conformation of heparin-derived tetrasaccharide

1996 ◽  
Vol 318 (1) ◽  
pp. 93-102 ◽  
Author(s):  
Dmitri MIKHAILOV ◽  
Kevin H. MAYO ◽  
Ioncho R. VLAHOV ◽  
Toshihiko TOIDA ◽  
Azra PERVIN ◽  
...  
Keyword(s):  
Chair Conformation ◽  
Coupling Constants ◽  
Solution Conformation ◽  
1H And 13C Nmr ◽  
Small Deviations ◽  
J Coupling Constants ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Dynamics Simulations ◽  
Ring Conformations

The solution conformation of the homogeneous, heparin-derived tetrasaccharide ΔUA2S(1 → 4)-α-d-GlcNpS6S(1 → 4)-α-l-IdoAp2S(1 → 4)-α-d-GlcNpS6S (residues A, B, C and D respectively, where IdoA is iduronic acid) has been investigated by using 1H- and 13C-NMR. Ring conformations have been defined by J-coupling constants and inter-proton nuclear Overhauser effects (NOEs), and the orientation of one ring with respect to the other has been defined by inter-ring NOEs. NOE-based conformational modelling has been done by using the iterative relaxation matrix approach (IRMA), restrained molecular dynamics simulations and energy minimization to refine structures and to distinguish between minor structural differences and equilibria between various ring forms. Both glucosamine residues B and D are in the 4C1 chair conformation. The 6-O-sulphate group is oriented in the gauche–trans configuration in the D ring, whereas in the B ring the gauche–gauche rotomer predominates. Uronate (A) and iduronate (C) residues are mostly represented by 1H2 and 2S0 twisted boat forms, respectively, with small deviations in expected coupling constants and NOEs suggesting minor contributions from other A and C ring conformations.

Structure assignment of some 3,4′-diquinolinyl sulfides studied by Nuclear Overhauser Effects, X-ray analysis and reactions with sodium methoxide

2010 ◽  
Vol 109 (10) ◽  
pp. 509-514 ◽  
Author(s):  
Stanislaw Boryczka ◽  
Andrzej Maślankiewicz ◽  
Miroslaw Wyszomirski ◽  
Teresa Borowiak ◽  
Maciej Kubicki
Keyword(s):  
Sodium Methoxide ◽  
X Ray ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Structure Assignment
Sign in / Sign up

Export Citation Format

Share Document